Lignin, which represents 15-35% of wood, is the most abundant renewable organic material on the earth. The pulping industry separates cellulose from the wood composition resulting in lignin and hemicellulose waste by-products known as black liquor and spent pulp liquor. In the sulphite process, the main by-product contained in the spent pulp liquor is lignosulphonate. With each ton of pulping products producing 330-540 Kg of lignosulphonate, the global annual production capacity of lignosulphonate is about 1.8-2.0 million tons. Most of the lignosulphonate (66%) produced in pulping industries is burned as fuel and 34% is treated and disposed. Using this waste stream as a fuel source is inefficient, and releases large amounts of pollutants such as SO2. Simple disposing of lignin, on the other hand, incurs a significant cost to the pulping industry.
Water sources for human and agricultural uses are struggling to meet the growing demand due to the increase in human population. Therefore there is a strong international trend to minimize the requirements of irrigation and water supply to agriculture by developing new types of economical, sustainable, naturally derived controlled release hydrogel fertilizers. Progress in this field will have remarkable impact on the agricultural food production efficiency, as well as environmental and economic benefits.